The invention relates to a process for the environmentally acceptable generation of electric energy in a combined gas/steam generating power plant by efficient expansion of a high-pressure working medium in a gas turbine and of high-pressure superheated steam of a fossil fuel fired steam generator in a gas turbine, as well as to a plant for performing the process.
In prior art processes for the combined generation of electric energy using gas and steam turbines, the compressed working gas generated in the oil or gas fired furnace chamber of the gas turbine is first efficiently expanded in the gas turbine at a temperature above 1,000.degree. C., and the hot turbine gases that still exhibit an oxygen excess are utilized as combustion air for the steam generation furnace. Compared to power generating plants working solely with steam, combined gas/steam generating power plants are characterized by improved efficiency and thus, related to output, lower CO.sub.2 emissions. The oxygen excess of the gas turbine is attributed to the fact that the generation of the mass flux needed for the gas turbine requires an air volume that greatly exceeds the actual combustion air volume. Since the combustion takes place in the furnace chamber with an oxygen excess and at high temperatures, the waste gases of the gas turbine contain a high portion of nitric oxides, thus requiring a suitable design of the flue gas denitrification system of the steam generator.
But the waste gases of the gas turbine also have a lower O.sub.2 content than fresh air. Compared to the use of fresh air for the steam generator furnace, this increases the waste gas or flue gas mass flux through the steam generator and following components, such as the electrostatic filter, upward draft, denitrification system, and flue gas desulfuration system by up to 50% for an identical steam generator output. This again increases the operating power consumption of the power plant system so that part of the improvement in efficiency resulting from the combination of gas turbine and steam generator furnace is again lost. In the case of melting chamber furnaces, an increase in the flue gas mass flux is in any case only possible to a limited extent, since one of the factors being influenced negatively is the melt flux in the furnace chamber. It is therefore not, nor only conditionally, possible to refit steam generating power plants with melting chamber furnaces.
It is thus the task of this invention to improve a process of the aforementioned type for generating electric energy in a combined gas/steam generating power plant so as to achieve both higher efficiency and thus reduce the specific CO.sub.2 emission and to reduce the nitric oxide emissions.